This invention relates generally to phase change memories.
Phase change memory devices use phase change materials, i.e., materials that may be electrically switched between a generally amorphous and a generally crystalline state, as an electronic memory. One type of memory element utilizes a phase change material that may be, in one application, electrically switched between generally amorphous and generally crystalline local orders or between different detectable states of local order across the entire spectrum between completely amorphous and completely crystalline states.
Typical materials suitable for such an application include various chalcogenide elements. The state of the phase change materials is also non-volatile. When the memory is set in either a crystalline, semi-crystalline, amorphous, or semi-amorphous state representing a resistance value, that value is retained until reprogrammed, even if power is removed. This is because the programmed value represents a phase or physical state of the material (e.g., crystalline or amorphous).
When a potential is applied across the phase change memory, conduction may occur. The greater the volume of phase change material that must be programmed, the greater the programming power requirements. Thus, a breakdown layer may be used which is subject to breakdown at a point between an electrode and the phase change material. Conduction may occur at this breakdown point, reducing the volume of material that needs to change phase.
A so-called glue layer may be used between the phase change material and an underlying insulator. If the breakdown layer intervenes between the glue layer and the phase change material, the glue layer's ability to adhere the phase change layer would be compromised.
Thus, there is a need for alternate ways to form phase change memories with both breakdown and glue layers.